نوع مقاله : مقاله پژوهشی

نویسندگان

1 استادیار دانشکده مهندسی نقشه برداری و اطلاعات مکانی، پردیس دانشکده های فنی، دانشگاه تهران

2 دانشیار دانشکده مهندسی نقشه برداری و اطلاعات مکانی، پردیس دانشکده های فنی، دانشگاه تهران

3 کارشناس ارشد ژئودزی، دانشکده مهندسی نقشه برداری و اطلاعات مکانی، پردیس دانشکده های فنی، دانشگاه تهران

چکیده

جهتگیری دقیق یک فضاپیما نسبت به زمین، خورشید یا هرکدام از سیارات، یکی از مشکلترین چالشها در فناوری فضایی است. سیستم تعیین و کنترل وضعیت یکی از مهمترین زیرسیستمهای ماهواره است. هدف اصلی طراحی این زیرسیستم انتخاب بهترین الگوریتم برای استخراج وضعیت کامل از فضاپیما با توجه به دقت یا زمان اجرا یا هر دو میباشد. هدف الگوریتمهای تعیین وضعیت، محاسبه جهتگیری فضایی ماهواره بر اساس سنسورهایی است که میتوانند اندازهگیریهای مقدار شناخته را در قالب بردارهای سهبعدی انجام دهند. در میان سنسورهای مورد استفاده برای تعیین وضعیت فضاپیما، ردیاب ستاره توانایی انجام توأمان عملیات تعیین موقعیت، وضعیت و برآورد سرعت زاویهای فضاپیما را با دقت بالا، حجم محاسبات بهصرفه و مدت زمان قابل قبول برای پروژههای فضایی دارد. این ردیاب در میان سایر حسگرهای تعیین وضعیت، به‌‌عنوان دقیقترین حسگر شناسایی شده و قابلیت تعیین وضعیت ماهوارهها با دقت مناسب حتی در مدارهای بالا را دارد. ردیاب ستاره از آسمان اطراف خود تصویربرداری مینماید. در بخش میکرو پردازنده این ردیاب، ستارگان موجود در تصویر اخذشده شناسایی میشوند و به این ترتیب مشاهدات موردنیاز برای انجام پروسه تعیین وضعیت حاصل میشوند. با شناسایی ستارههای تصویر شده و دادههای چارچوب مرجع اینرشیای مربوطه، وضعیت فضاپیما با استفاده از الگوریتمهای تعیین وضعیت مانند TRIAD  و برآوردگر کواترنیون (QUEST) و ... تعیین خواهد شد. در این تحقیق هدف پرداختن به فرآیند تعیین وضعیت فضاپیما و خصوصاً بررسی و مقایسه الگوریتمهای تعیین وضعیت، و سپس انتخاب مناسبترین الگوریتم تعیین وضعیت با استفاده از مشاهدات ردیاب ستاره میباشد.  براساس ارزیابی­های انجام شده نتایج حاصل از الگوریتمهای TRIAD و QUEST با روش Shuster بالاترین دقت را در بین نتایج هشت الگوریتم دیگر کسب کردند.

کلیدواژه‌ها

عنوان مقاله [English]

Evaluation of attitude determination methods using Star Tracker Observations

نویسندگان [English]

  • Saeed Farzaneh 1
  • Mohammad Ali Sharifi 2
  • Seyedeh Samira Talebi 3

1 Assistant Professor, School of Surveying and Geomatics Engineering, Faculty of Engineering, University of Tehran, Iran

2 Associate Professor, School of Surveying and Geomatics Engineering, Faculty of Engineering, University of Tehran, Iran

3 Msc in Geodesy, School of Surveying and Geomatics Engineering, Faculty of Engineering, University of Tehran, Iran

چکیده [English]

Extended Abstract
Introduction
In recent years, the development of the country in the space industry and the ability of building, launching and infusion of satellites in the lower orbit has put the limited number of countries with such technology. In order to complete the entire cycle of the space industry, the satellite navigation and control, which has been neglected since the beginning of the movement of space science in the country, has to be considered specially. The attitude determination in one sentence is the application of a variety of techniques for estimating the attitude of spacecrafts. In dynamic astronomy, the attitude determination is the the process of controlling the orientation of an aerospace vehicle with respect to an inertial frame of reference or another entity such as the celestial sphere, certain fields, and nearby objects, etc.
 A spacecraft attitude determination and control system typically uses a variety of sensors and actuators. Because attitude is described by three or more attitude variables, the di®erence between the desired and measured states is slightly more complicated than for a thermostat, or even for the position of the satellite in space. Furthermore, the mathematical analysis of attitude
determination is complicated by the fact that attitude determination is necessarily either underdetermined or overdetermined.
 
Materials and methods
Attitude determination typically requires finding three independent quantities, such as any minimal parameterization of the attitude matrix. The mathematics behind attitude determination can be broadly characterized into approaches that use stochastic analysis and approaches that do not. This paper considers a computationally efficient algorithm to optimally estimate the spacecraft attitude from vector observations taken at a single time, which is known as single-point or single-frame attitude determination method. There have been a number of attitude determination algorithms that compute optimal attitude of a spacecraft from various observation sources (known as the Wahba’s problem), and each of the methods has advantages and limitations in terms of accuracy and computational speed. The most popular are: the very important ˆq-Method, the most popular TRIAD and QUEST, SVD, FOAM, and ESOQ-1, the fastest ESOQ-2, and many others approaches introducing new insights or different characteristics, for instance, the EAA, Euler-2, Euler-ˆq, and OLAE.
 
Results and discussion
Since star detection algorithms can provide more than two stars, the star detector field of view often consists of two or more stars that are passed through the identification algorithms will be detected, those star vectors that have measurement errors can be compensated by using more than two stars. Methods such as the QUEST algorithm usually optimize an error function to the minimum optimal. In fact, the QUEST algorithm estimates the optimum specific eigenvalue and vector for the problem described in the Q_method method without the need for complex numerical calculations. The fact that the QUEST algorithm retains all the computational advantages of a fast definitive algorithm while maintaining the desired result efficiency underscores why it is typically used.
 
Conclusion
Simulation results showed that the traid and quest algorithms with shuster method attitude determination algorithm can be an efficient alternative over the eight tested algorithm in terms of computational efficiency for singularity-free attitude representation.

کلیدواژه‌ها [English]

  • Spacecraft attitude determination
  • Star tracker
  • Star identification algorithm
  • Attitude determination Algorithm
  • Quaternion
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